1. Field of the Invention
The present invention relates to an apparatus and a method for keyword outputting.
2. Description of the Related Art
There are strong needs to know popular topics and current event information. Various techniques to meet the needs have been developed. Among them, attention is paid to techniques of extracting current event keywords using document information to know topics or current event information. For example, in a Web search engine as a technique on the Web, attention is paid to the above techniques as techniques that allow to know needs for various kinds of information in the world in the form of search keywords and to known daily topics.
As a technique of extracting news which is a topic in a certain period, there is available a technique of displaying the rank information of keywords found on the Web. This technique generates search ranks on the basis of frequencies in a certain period, and displays, as the sign of a topic, a keyword commonly contained in entries recently added by a blog search engine or the like.
Kizasi.jp (“searched Jul. 26, 2006”, Internet <URL: kizasi.jp/>), which is the Web site for finding a sign of change from an infinite number of words written in blogs, describes a technique of displaying currently hot keywords in accordance with the frequencies of keywords written in Web sites (known as blogs) on the Internet on which individuals post their diaries and remarks. A keyword presented by such a technique is a kind of keyword indicating current event information. In kizasi.jp, keywords indicating current event information can be presented for every predetermined time such as 24 hr, one week, or one month, in a rank form.
The keyword extraction method disclosed in JP-A No. 2001-325272 (KOKAI) attempts to present topics by clustering new words.
The homepage kizasi.jp also describes a technique of presenting not only keywords exhibiting high frequencies (keywords indicating current event information) for a predetermined period of time but also keywords associated with the keywords indicating the current event information. However, kizasi.jp is not configured to present information indicating how a given topic progresses upon presentation of the topic. That is, if there are a plurality of subtopics associated with one big topic, the above technique does not allow the user to know the kinds of subtopics included in the big topic and the times at which and the order in which they appear. Assume that “◯◯ injury case” is extracted as a keyword indicating current event information, and “case occurrence”, “placed on wanted list”, and “criminal arrest” are extracted as keywords associated with the keyword. The homepage kizasi.jp is not designed to control a display order in accordance with the newnesses and appearance periods of keywords or control keywords by visualizing the progression of a topic. For example, subtopics of the big topic “◯◯ injury case” can be seen as “case occurrence”, “placed on wanted list”, and “criminal arrest”. In this case, these subtopics are preferably displayed in the order of “case occurrence→placed on wanted list→criminal arrest”. However, kizasi.jp does not perform such display control. In the first place, the user cannot grasp that the keywords indicating the subtopics constituting the big topic “◯◯ injury case” are “case occurrence”, “placed on wanted list”, and “criminal arrest”. It is therefore impossible to obtain a policy of how to determine a search query for searching for an appropriate news article from the Web.
The technique disclosed in JP-A No. 2001-325272 (KOKAI) performs clustering processing upon extraction of keywords. In some cases, therefore, no consideration is given to a context in which a keyword appears. As a consequence, the same keyword may be contained in a totally different topic.